Process for manufacturing plywood tubing



Sept. 14; 1948. J. .1. DUNNE ETAL 2,449,526 PROCESS FOR MANUFACTURING PLYWOOD TUBING Filed May 3. 1943 INVENTORS JJflU/WVE ATTORNEYS Patented Sept. 14, 1945 PROGESS FOR MANUFACTURING PLYWOOD TUBING James J. Dunne. Westport. Conn., and Orvil 8. Tattle, New Rochelle, N. Y., asslgnors to United States Plywood Corporation, New York, N. Y.,

a corporation of New York Application May 3, 1843. Serial No. 485,478 s Claims. (01. 154-83) The present invention relates to the manufacture of plywood pipes and tubing of seamless construction, and is an improvement on the process and product described in the copending application of Theodore E. Ilch, Serial No. 457,894, filed September .10, 1942, Patent No. 2,411,542, dated November 26, 1946.

As in such copending Ilch application. the

term "seamless is to be understood to mean a construction in which no seam or Joint between the ends of the individual'veneers of which the tube is composed extends continuously in the radial direction from the interior to the exterior of the tube, the seams being suitably staggered to cause a solid mass of wood veneer. preferably composed of all the remaining veneer units, to

overlie and/or underlie the seam or Joint in any particular veneer unit.

In the process described in the abovementioned Ilch application, individual veneer panels, cut to suitable dimensions, are coiled by hand about a longitudinal axis until the ends overlap to a greater or less extent, the temporary tube being thus of a diameter less than the final diameter. and the tube then inserted endwise into a longitudinally slit mandrel which has previously been contracted by suitable clamps to a diameter less than its normal diameter, and allowed to expand within the mandrel, whereupon the veneers as-.

sume a cylindrical shape with the ends in abutting or slightly overlapping relation, the width of the veneer sections being so cut that the ends do not overlap in the finished pipe. The successive veneers are inserted in such manner that the seams or joints are in staggered relation. The veneers are coated with a suitable thermosensitive adhesive (except the inside face of the innermost veneer layer and the outer face of the outermost veneer layer) and after the plywood tubing has been built up to the desired thickness, the veneers are subjected to heat and pressure applied by means of a pliable or expansible fluid-tight membrane or bag inserted inside of the plywood tub ng. The heat causes the adhesive to fuse and the applied pressure molds the veneers against the inside of the mandrel until a compact plywood tubing is formed. Ifthe adhesive is of the thermo-plastic type, the plywood tubing is then allowed to cool before the clamps are removed from the mandrel. the latter being thereby allowed to expand to its normal diameter, and the plywood tubing then removed;

if the adhesive is of the thermo-setting type, the.

clamps about the mandrel canbe released and the plywood tubing can be removed while still quite hot. The veneer sections are of progressively smaller width, to produce tube elements of increasingly smaller diameter as the building up of the plywood tubing progresses, so as to avoid overlapping of the ends of any particular veneer tubing; and the directionof the grain of the veneers is varied in the several tubular layers to produce the desired vertical crushing strength and hoop strength, the latter being important especially where'the tube is to be employed as a conduit for fluids under pressure.

The coiling of the veneers is done by a gang of workmen distributed along the length of the veneersection, and it has been found in practice that this manual-operation on the thin veneers results frequently in tearing the veneers.

interrupts the regular work ng procedure. Also,

coiling by hand ofeach individual veneer which I is to be used in building up the plywood tubing, whichmay have as many as fifteen and even more veneer sections, is a laborious and timeconsum ng operation.

It is the general object of the present invention to provide an improved procedure wherein the over-all time required forcharging a man-. drel with the requisite number of veneers, from the moment of beginning work on the individual veneers to the moment in which the built-up plywood tubing in the mandrel is ready for receiving the pressure and heat-applying membraneor bag. is considerably reduced, and the output correspondingly increased.

It is a further object of the invention to provide an improved process wherein breakage or tearing .of the veneers during the operation of preliminary coiling is greatlyreduced and even practically eliminated, and the economy of the process thereby further increased.

It is a still further object of the invention to improve upon th known process by reducing the amount ofmanuallabor required to build up plywood' tubing within the mandrel.

Other objects of the invention willappear from the following more detailed descr iptioni' 'v and ithe features of novelty will be setgout in the appended claims. t According tothe present invention .eneers are not coiled individually, but in ,pairslwith the grain of onerunning at an angle to. the grairrof the other veneer. Theveneers are united-to each other, for example,,by,a bond of adhesive,or;in anyother suitable manner for example, bymeans of staples, but highly satisfactory results have the been obtained by the use of an adhesive. There I This not only causes a loss of the veneer itself, but

is formed in this way what we shall hereinafter refer to as a double veneer, and it is an important feature of this elemental veneer construction that each veneer sheet strengthens and iortifies the other, so that when the double veneer is coiled, there is-little tendency to tearing or breaking, even if one of the veneer sheets has its grain running at right angles to the axis of the cylinder into which the veneers are coiled.

A two-ply veneer is not, so far as we are aware, an article of commerce. Basically, it has the fault which a plywood construction is designed to eliminate; namely, it is an unstable or un-. balanced structure and tends to curl if left to itself. This curl may be either about an axis parallel to the longitudinal median line of the panel, or at an angle thereto; and even where no curl is present immediately after manufacture, a curl usually soon develops upon change in the moisture content of the veneer plies. So far as we have been able to ascertain, no commercial use has been made of such a two-ply or double veneer.

The present invention utilizes to advantage the normal tendency of a double veneer, in which the grains run at angles to each other, to curl: for in accordance with our process, the original curl is utilized in coiling the double veneer into the cylindrical form. The initial bending or coiling operation is thus facilitated by the original curvature of the double veneer. A further advantage flowing from the use of our double veneers resides in the fact that a large number of such double veneers can be simultaneously manufactured-in a press, whether heated by steam, by electro-static induction, or otherwise. The labor involved in manufacturing a single veneer unit is considerably less than the labor required to coil and insert the second veneer in the process described in the application above mentioned. There is furthermore less loss in handling the double veneers than in the more frangible single veneers.

The further details of our process will be described in connection with the attached drawing. wherein Fig. 1 shows a section of a double veneer constructed in accordance with the invention:

Fig. 2 is an end view of the double veneer show- I 'ing the spontaneous curl thereof which is taken advantage of in our improved process, the thickness being shown somewhat exaggerated for greater clearness.

. Figs. 3 and 4 show double veneers with the grains running in different directions; and

Fig. 5 is a vertical section with parts in elevation of a mandrel containing the built-up plies of double veneers and heated and pressed against the mandrel by a pliable or expansible bag contacting afluid, such as saturated steam, at suitable temperature and pressure.

- The double veneers employed in the present invention are preferably manufactured, as already indicated, by bonding together two veneers IO, N, with their grains running at an angle to each other by means of an interposed layer of a flexible. thermo-sensitive, for example,thermo-plastic tion or panel are preferably scarfed as indicated at l2 to provide an overlapping Joint. After removal from the press, in which the veneers are form with the ends overlapping to some extent.

When so coiled, the double veneer is inserted into a mandrel, for example, of the type shown in the copending application above referred to, and shown in section at i3. of the attached drawing. A plurality of double veneers are employed in building up a tube or pipe; and the successive double veneer panels used in making up the successive coiled cylinders are of progressively decreasing width to allow for the decreasing width of the pipe or tube as the center is approached. The width of the double veneer panels is such that 'even though the longitudinal ends overlap to some extent after the cylinders, upon release, spring into position against the mandrel or against the previously inserted cylinder, there will be no overlapping except over the scarfed edges.

after the cylinders have been further expanded against the mandrel upon the application of heat and pressure by means of a flexible or expansible fluid-tight bag l4. Ascan be seen from Fig. 5,

the joints of the several panels of double veneer I are staggered. in relation to each other, so that there is no continuous Joint from the interior of the formed plywood tube to the exterior thereof, as indicated at I5. It will be understood that the mandrel if, during the application of the heat and pressure, is in a contracted condition, brought about by clamps i6; and the mandrel can be contracted either before the insertion of the coiled double veneers, or after such insertion, but before the application of the heat and pressure by way of the bag l4. While the scarfed edges are indicated in Fig. 5 as being in perfectly fitting relationship, in actual practice, there may be a slight gap between the facing edges in at least certain instances; in no case, however, should there be any overlapping of the full thickness of any double veneer. Even in the contracted condition, the mandrel is, however, not completely closed, a small gap i5a being allowed to remain to permit the escape of vapors, gases, etc. Before the application of the heated fluid under pressure, the mandrel is positioned upon a cradle 11 within a casing l8, but as these structures form no part of the present invention, they have not been shown in detail.

It will be understood that before the double veneers are inserted within the mandrel, they are provided with a thermo-sensitive adhesive, for example, a thermoplastic resin, upon one face or upon both faces, as the case may be, depending upon whether the particular double veneer constitutes on the one hand the outermost or innermost ply, or an intermediate ply. This adhesive may be of the thermo-plastic type above referred to, but is preferably of the thermo-setting type. so that the mandrel can be released and the plywood tubing removed while it is still quite hot, without danger of separation of the double veneers from each other. The thermo-setting adhesive should be of the type which remains fluid throughout the intervalrequired for all the layers of thermo-setting adhesive to bebrought to the proper activating temperature, so thatthe several double plies will all be in a condition to be s'hiited relatively to each other at the same time and proper molding thereby assured. Any resin having a long period of fluidity before it finally sets is preferred. Various phenol formaldehyde resins could. however, also be employed provided that the resin is selected in dependence on the rate of heat conduction from the innermost to the outermost double veneer. Of course, where the fusion of the resin is effected by electrostatic induction, the matter of rate of heat conduction is of no moment and thermo-setting resins having only a short period of fluidity can be employed.

The grain of the two veneers constituting a double veneer may run at various angles, as indicated in Figs. 3 and 4; and it is not necessary even that any grain run parallel to the axis of the tube. The arrangement of the grains will depend upon the tube characteristics desired, and will be based upon principles well understood in the art, Thus. the grains of each particular double veneer may run at 90. 45, or at any other angle to each other. It will be understood that where the circumference of the formed tube is greater than the width of the veneers available in any particular Wood, several sections of veneer may be united in any suitable manner, as by edge to edge bonding, in well lcnown manner.

Variations from the specific materials. and procedures above described will occur to those skilled in the art without departing from the principles of the invention. Thus, the two-veneers of the double veneer may be provided with an intervening, thermo-sensltive layer of adhesive and be held together suhlciently strongly with a temporary adhesive like ordinary glue applied at spaced areas to permit the rolling operation, the two piles of each double veneer being then permanently bonded together at the same time that the several double veneers are bonded and molded to each other within the mandrel. We have found, however, that best results are obtained by first permanently uniting the two veneers of each double veneer. Also, certain advantages of our invention could be obtained by the use of veneer unit composed of three plies of veneer, but such a structure is first of all usually balanced and, therefore, will not provide the initial curl which aids greatly in rolling the veneer unit into the cylindrical form. The three-ply veneer would also be much more difficult to use, except perhaps for pipes of very large diameter. Also, double veneers can be combined in any suitable relation with single ply veneers but the advantages of our pand in the casing and assume approximately the invention will be reduced to a corresponding extent. It will further be evident that the edges of the double veneers could be cut rectangularly instead of scarfed or in any other fashion.

It has been stated above that the double veneers can be made using a thermoplastic adhesive such as polyvinyl butyral resin. A perfectly satisfactory double veneer can also be made using a thermosetting adhesive or using any good phenoliormaldehyde resin adhesive.

It is also satisfactory to use a thermoplastic adhesive on the faces of the double veneers in place of the thermosetting adhesives described above. For example, an adequate thermoplastic adhesive would be obtained if a fliteen per cent solution of polyvinyl butyral resin dissolved in ethyl the double veneer and allowed to dry before bein inserted i h n e mandrel.

contour of the casing. each double-pl being composed of two thin sheets united to each other with the grain or one running at an angle to that of the other. there being provided a layer of thermo-sensitive adhesive between the adjoining faces of adjacent double-plies, applying a tubular membrane interiorly of the assembled sheets, distending the membrane with a heat and pressure medium to a degree suflicient to press the sheets against the interior of the casing to bond the double-plies to each other and to mold the doubleply assembly to the configuration of the casing.

2. The method of forming an integral molded i seamless plywood tubing from wood veneers. which comprises applying athermo-sensitive adhe sive to a plurality of double-ply wood veneers, each of said double veneers being composed of two wood veneer layers united to each other with the grain of one running at an angle to that of the other, introducing successively narrower strips of such double-ply veneers'one by one into a relatively rigid cylindrical casing through one end thereof, applying an expansible membrane interiorly of the assembled double-pay veneers, and distending the membrane with a heated medium at a pres sure sufllcient to press the veneers outwards against the interior of the casing to mold them into a seamless plywood tubing.

3. Process for the manufacture of seamless, multi-ply tubing of considerably greater length than diameter, which comprises coiling a doubleply of flexible fibrous material to an average outside diameter less than the average outside diameter of the finished tube, the double-ply being composed of two sheets of said fibrous material united to each other with the grain of one running at an angle to that of the other, inserting the so coiled double-ply endwise into a long, relatively rigid tubular mandrel having inside transverse dimensions substantially equal to the outside transverse dimensions of the finished tube, and allowing the coiled double-ply to expand within the mandrel and assume a tubular contour similar to that of the mandrel interior and substantially free from pressure stresses in the peripheral direction, similarly coiling and individually and successively inserting into the mandrel in endwise iashion an additional double-ply or double-plies of said fibrous material united asv aforesaid, the subsequently coiled double-plies being allowed to. expand against the previously inserted double-ply within the mandrel, there being provided a layer of adhesive between adjacent double-plies. then heating the assembled doubleplies and applying fluid pressure from the interior oi the mandrel outwardly against the so telescopeol fibrous tubes to cause activation oif the ad- 'hesive and mold the sheets of fibrous material against the interior surface of the mandrel and into an integral multi-double-ply tube, and removing the flbrous tube from the mandrel.

a. Process according to claim 2, wherein the longitudinal edges of the double-ply veneers are scaried prior to coiling to provide scarfed Joints double-ply veneers to suitable dimensions, each double-ply bein composed of two thin sheets united to each other with the grain of one running at an angle to that of the other, coiling, in

succession, such individual cut double-ply veneers about a longitudinal axis until the longitudinal edges overlap, the temporary tubes thus produced being of a diameter less than the final diameter of the molded seamless plywood tube to be produced, inserting such temporary tubes endwise and in succession into a tubular mandrel, permitting the veneers to expand within the mandrel whereby they assume a tubular shape with the longitudinal edges of each double-ply veneer tube in contiguous relation, there being provided a layer of thermo-sensitive adhesive between the adjoinin faces of adjacent double-ply veneers, inserting a flexible fluid-tight tubular membrane inside the assembled double-plies within the mandrel, applying heat and sufiicient pressure by means of said membrane to the built-up double-plies to cause the activation of the adhesive and thereby mold the assembly of double-plies into an integral plywood tube having external dimensions corresponding to the interior dimensions of the mandrel, and removing the molded seamless plywood tube from the mandrel.

'7. Process for the manufacture of seamless plywood tubing, which comprises cutting individual veneer units to suitable dimensions, each unit comprising two thin veneers bonded to each other by an intermediate layer of adhesive, said double-ply veneers being rovided upon certain of their outer surfaces with a thermo-sensitive adhesive, coiling, in succession, such individual cut double-ply veneers about a longitudinal axis until the longitudinal edges overlap, the temporary tubes thus produced being of a diameter less than the final diameter of the molded seamless ply- \vood tube to be produced, inserting such temporary tubes endwise, and in succession, into a perforated tubular mandrel with their longitudinal joints in staggered relation, permitting the double-ply veneers to expand within the mandrel whereby they assume a tubular shape with the longitudinal edges of each double-ply in contiguous relation, inserting a flexible fluid-tight tubular membrane inside the assembled double-plies within the mandrel, applying heat and sufllcient pressure by means of said membrane to the builtup veneers to cause activation of the adhesive and file of this patent:

thereby mold the assembly or double-plies into an integral plywood tube while venting air and vapor through the mandrel, and removing the molded seamless plywood tube from the mandrel.

8. Process for the manufacture of seamless plywood tubing, which comprises coiling a wood veneer unit to an average outside diameter less than the average outside diameter of the finished tube, each unit comprising two veneers-united to each other by an intermediate layer of a flexible adhesive, inserting the so coiled double-ply veneer unit endwise into a relatively rigid tubular mandrel having inside transverse dimensions substantially equal to the outside transverse dimensions of the finished tube, allowing the coiled doubleplies to expand within the mandrel and assume a tubular contour smaller than that of the mandrel interior and substantially free from pressure stresses in the peripheral direction, coiling and individually and successively inserting into the mandrel in endwise fashion an additional doubleply veneer unit or units, such last-mentioned individual coiled double-plies being each allowedto expand against the previously inserted doubleply within the mandrel, there being provided a layer of adhesive between adjacent double-plies, and then heating the veneers and applying fluid pressure from the interior of the mandrel outwardly against the so telescoped double-ply tubes to cause activation of the adhesive, and mold the double-ply aggregate against the interior surface of the mandrel and into an integral multi-double-ply tube, and removing the plywood tube from REFERENCES cr'rEn The following references are of record in the UNITED STATES PATENTS Niunber Name Date 51,735 Mayo Dec. 26, 1885 601,993 Wittkowsky Apr. 5, 1898 612,897 Ellis Oct. 25, 1898 1,595,811 Anderson Aug. 10, 1926 1,595,856 Clark Aug. 10, 1926 1,645,936 Schlesinger Oct. 18, 1927 2,043,026 Arnold June 3, 1936 2,090,415 Homey Aug. 17, 1937 2,223,587 Verhey Dec. 3, 1940 2,279,820 Hamilton Apr. 14, 1942 2,296,781 Farny Sept. 22, 1942 2,312,333 Gramelspacher Mar. 2, 1948 FOREIGN PATENTS Number Country Date 637,029 Germany Oct; 21, 1986 

